Determination of antibody concentration as the main parameter in a dengue virus antibody-dependent enhancement assay using FcγR-expressing BHK cells.

Dengue virus (DENV) causes a life-threatening illness, with a wide range of symptoms from mild febrile illness, dengue fever (DF), to life-threatening illness, dengue hemorrhagic fever (DHF). Antibody-dependent enhancement (ADE) is considered to be a risk factor for DHF. In the present study, we determined the parameters for ADE assays using FcγR-expressing BHK cells. Monoclonal antibodies and human serum samples were used in the assays. We examined antibody concentration and virus concentration and analyzed whether antibody concentration or DENV-antibody ratio determines ADE activity. Virus growth was quantified by a conventional plaque titration method using FcγR-expressing BHK cells. The assay allowed the detection of DENV growth with inoculation doses ranging from 10(2) PFU/ml to 10(6) PFU/ml using monoclonal antibodies and undiluted or diluted serum samples. The results indicate that antibody concentration rather than DENV-antibody ratio determines the demonstration of ADE activity. Thus, antibody concentration rather than multiplicity of infection was defined as the main determinant in ADE assays using FcγR-expressing BHK cells.